1. Field of the Invention
The present invention relates to a method and apparatus for weighing products and, more particularly, for weighing products that are moved using a conveyor by first lifting the product above the conveyor and then measuring the weight of the lifted product.
2. Background Art
Quality control has always been integral to successful operation of an industrial manufacturing and shipping facility. It is, obviously, important to provide the customer with the correct quantity of goods both for the customer's satisfaction and for the highest possible efficiency of the facility. A common method for ensuring that the correct quantity of goods are loaded and shipped to the customer is by weighing the box or container in which the goods are packed.
Many of the packaging lines currently used rely heavily on automation and less on human intervention. However, since there are occasions when the wrong amount of a product is placed into a bag, carton, or other container, or the wrong number of bags, cartons, or other containers are loaded into the final shipping container, a product weigher is a way to ensure that the correct product weight is being shipped to the customer.
There are a number of prior art devices used to weigh the shipping containers on a packaging line. These commercially-available devices often consist of a conveyor belt approximately thirty inches long and twenty inches wide. As the shipping container traverses over load cells below the conveyor at a weighing station, the load cells transmit to a main control board the weight of the conveyor plus any product being conveyed. Digital filters located on the main control board filter out dynamic signals that occur as a result of weighing a moving object.
However, when measurements are taken on a moving conveyor belts, as in the prior art systems, complex digital filtering must be applied to the analog signal to remove dynamic components in the signal. These systems often are very proprietary to the equipment manufacturer and are not easily understood by the end user. Moreover, the prior art systems are difficult to interface with other equipment and supervisory data collection computers. Still another problem is that since the conveyor is part of the load being weighed, the conveyor must be made as light as possible, resulting in a conveyor design that, in many cases, does withstand an industrial environment well.